Many high power applications use switching power supplies, in part due to the small area and volume they occupy. Converters used for a typical switching power supply include active components and passive components. For high power applications, the active components are discrete, not integrated, because of the difficulty associated with integrating high power components and controlling heat dissipation.
Switching power supplies have a number of problems associated with them. For example, the switching supplies require power MOSFETs to handle the high currents required by the high powered applications. These MOSFETs are significantly larger than typical MOSFETs, and have high parasitic capacitances associated with them, which reduce the overall performance of the system. Further, the highly specialized drivers to the drive the large gate-to-source capacitance of power MOSFETs must be very well controlled. If the drivers are not well controlled, unnecessary capacitive switching losses are introduced into the system.
Switching the power MOSFETs on and off also requires large currents, which creates a significant amount of system noise through coupling and ground return path parasitics. The large currents provided to the MOSFETs also create a drop in the power supply, preventing the MOSFETs from turning on completely until the power supply has recovered. The drop is due, in part, to the parasitic inductance of the decoupling capacitor, which provides the instantaneous power required to activate the MOSFETs.
In addition, the MOSFETs are timed to ensure that one is fully off before the other turns on, creating a large non-overlap time and causing losses to power efficiency. The timing between turning oil one transistor and turning off another are set up to minimize shoot-thru current, which occurs when both transistors are on. This is done by ensuring that one FET is fully off before turning oil the other FET, which is controlled by non-overlap logic. In discrete power stages, the non-overlap time can be significant, causing loss in power efficiency because the output current must be provided by a diode during the non-overlap time.